In the making of blow molded plastic articles utilizing blow molding machines, a hollow plastic parison of molten plastic material in the form of a tube is extruded between two complementary blow mold halves, the blow mold halves are closed and the tube is blown to the confines of the mold by utilizing a needle that pierces the tube and air is introduced into the interior of the tube through the needle to form the article such as a hollow container. One commercially successful arrangement is of the type shown in U.S. Pat. Nos. 3,737,275 and 3,873,661 wherein a movable needle is first advanced by air pressure to penetrate the extruded plastic tube and air is thereafter applied through a bore in the needle to inflate the tube. After blowing, the blowing air is exhausted and the blow needle is withdrawn. Such an arrangement not only uses multiple parts but also requires critical timing to provide for the movement of the movable needle.
Among the objectives of the present invention are to provide a method and apparatus wherein does not require a movable needle; which has no moving parts; which is simpler to construct and maintain; which is less costly; which reduces mold costs by utilizing simplicity of placement, design and manufacture; which has less downtime; which is more reliable; which is more readily maintained; and which facilitates process start up.
In accordance with the invention, the method and apparatus utilizes one or more fixed needles and one or more micro vents associated with the blow mold cavity. Each needle has a first passage associated therewith through which vacuum is supplied to pull the molten plastic about the needle and a second passage therein through which air under pressure is introduced to tear the plastic and blow the container to the confines of the mold which has been closed about the plastic parison. Micro vents facilitate exhausting air which is about the parison. Preferably the second passage for compressed air is provided by a central bore and the first passage for the vacuum is provided by an annular space about the fixed needle. In a modified form, the fixed needle comprises dual air passages. Provision is made for utilizing plural molds with controls for supplying air and vacuum.